Conclusion 191 



a real difficulty that few other characteristics (except 

 fission rate) can be measured, for the purpose of cor- 

 relating them with it. 



This interrelation of diverse activities is brought out 

 in various experiments which have been described in 

 detail (as in figures 21, 28, 41, 46). Subjection to a 

 new set of environmental conditions does not wipe out 

 a particular activity and leave the rest untouched. In- 

 stead, it modifies quantitatively, not one activity, but 

 several of them. The organism does not put one ac- 

 tivity above all others. Neither the rate of growth nor 

 the frequency of fission nor the attainment of a certain 

 size has an inviolable right-of-way; instead, each of 

 them compromises with the others. Assimilation 

 which is inadequate to maintain a standard rate of 

 growth is cooperated with by a retardation in the on- 

 set of fissioning. This sort of picture is familiar to 

 every student of the functioning of living objects. 



Racial regulation. Every individual is responding 

 to a complex of factors resulting from past generations 

 as well as of factors immediately impinging. For this 

 reason it is not surprising that the whole interplay of 

 characteristics is not completely upset or destroyed by 

 a change in one environmental factor, such as lack of 

 food or low tension of oxygen. Each individual has 

 a certain momentum from its race. This shields it 

 from being completely dominated by immediate condi- 

 tions; it also adds to the factors controlling the char- 

 acter which is being studied. To find whether a given 

 condition has influence is easily accomplished by keep- 

 ing everything else constant. But to find how the 

 factors interact to constitute a regulation, requires a 

 highly complicated experimental analysis. It has not 

 been carried out for any biological regulation; for the 

 particular one of the regulation of size it is only 

 possible at the present time to visualize simultaneously 



